This invention relates to olefin polymerization catalysts and more particularly to improved catalysts for the polymerization of propylene and higher alphaolefins.
Olefin polymerization catalysts based on transition metal compounds and aluminum alkyls are well known in the art. Particularly, the use of titanium trihalide compounds to produce crystalline propylene polymers has been reported widely. Among recently published catalytic systems based on titanium trihalides are U.S. Pat. Nos. 3,984,350; 4,210,738; 4,210,729; 4,210,736; and European Patent Application No. 79301996.9 published as Number 0 011 914 based on U.S. Ser. No. 945,929 filed Sept. 26, 1978, now U.S. Pat. No. 4,295,991; all of these references are incorporated herein by reference.
U.S. Pat. No. 4,210,738 describes a titanium halide-based catalyst in the delta crystalline form and having a color tending toward violet made by reducing titanium tetrachloride with an aluminum alkyl, treating the reduced solid with an ether, thioether or thiol complexing agent and reacting with additional titanium tetrachloride.
U.S. Pat. No. 4,210,729 describes a method to preactivate the catalyst described in U.S. Pat. No. 4,210,738 with a metal organic compound of Groups Ia, IIa, IIb, or IIIa.
U.S. Pat. No. 4,210,736 describes catalysts such as those listed in U.S. Pat. No. 4,210,738 which have been dried.
U.S. Pat. No. 3,984,350 describes a highly catalytically active titanium trihalide composition in the beta crystalline form having a brown color formed by reducing titanium tetrachloride with an aluminum alkyl and reacting, under controlled conditions, the resulting reduced product with a complexing agent and additional titanium tetrachloride.
European Patent Application Publication 0 011 914 describes a method to treat a catalyst such as described in the above-cited U.S. Patents with olefin monomer such that the resulting catalyst particle is non-friable. The method disclosed in the European Patent Application comprises contacting a reduced titanium trihalide composition with olefin monomer, such as propylene, before reacting with a Lewis base complexing agent and either titanium tetrachloride or a chlorinated hydrocarbon.
U.S. patent application Ser. No. 196,012 filed Oct. 10, 1980 now U.S. Pat. No. 4,324,693, assigned to a common assignee and incorporated by reference herein, discloses an improved olefin polymerization catalyst prepared by reducing titanium tetrachloride with an aluminum alkyl, contacting the resulting reduced solid with a pretreatment amount of alpha-olefin monomer under polymerization conditions and reacting the resulting product with a Lewis base complexing agent in a molar ratio to the reduced titanium compound of greater than 1.15 to 1 and additional titanium tetrachloride. In addition, a mixed Lewis base complexing agent comprising isoamyl ether and n-butyl ether was found advantageous.
Recently, olefin polymerization in the gas-phase has been reported. Such gas-phase polymerization is advantageous in that no liquid diluent is needed in the polymerization process. However, catalyst systems designed for other polymerization processes do not always work satisfactorily in gas-phase polymerization.
Catalysts prepared according to the above-cited references generally are active propylene polymerization catalysts. However, there is a need to increase the activity of such catalysts, while maintaining their ability to produce highly crystalline polymer, for use in advanced polymerization processes such as the gas-phase olefin polymerization process. The invention disclosed herein produces a significantly greater alpha-olefin polymerization catalyst activity together with polymer containing low hexane extractables in gas-phase polymerization.